There has heretofore been known a construction machine comprising an engine, a hydraulic pump configured to be driven by the engine, and a hydraulic actuator configured to be operated by hydraulic oil discharged from the hydraulic pump.
This type of construction machine is equipped with a radiator for cooling coolant water for cooling the engine (target fluid), and an oil cooler for cooling hydraulic oil led out of the hydraulic actuator (target fluid).
As a device usable as each of the radiator and the oil cooler, there has been known a heat exchanger described, for example, in the following Patent Literature 1.
FIG. 9 is a sectional view enlargedly depicting a part of the heat exchanger described in the Patent Literature 1.
The heat exchanger 101 described in the Patent Literature 1 comprises: an inlet-side tank 102 into which a target fluid to be cooled is led through a non-depicted inlet port thereof; an outlet-side tank 103 out of which the target fluid is led through a non-depicted outlet port thereof; and a plurality of tubes each fluidically connecting the inlet-side tank 102 to the outlet-side tank 103 (in FIG. 9, two 104A, 104B of the plurality of tubes are depicted).
The inlet-side tank 102 is a container extending along a given axis (an axis extending in a rightward-leftward direction in FIG. 9). Specifically, the inlet-side tank 102 has a sidewall 105 extending along the axis and surrounding the axis; and a pair of end walls 106 closing, respectively, two openings at opposite ends of the sidewall in a longitudinal direction of the inlet-side tank 102 along the axis (in FIG. 9, only one of the end walls 106 is depicted). The sidewall 105 is formed with a plurality of through-holes 105a which are arrayed in a line along the longitudinal direction (in FIG. 9, two of the plurality of through-holes 105a are depicted).
The outlet-side tank 103 has a configuration similar to that of the inlet-side tank 102. The two tanks 102, 103 are arranged such that respective axes thereof extend in parallel relation to each other, and respective sets of the plurality of through-holes 105a thereof are symmetrically opposed to each other.
The tube 104A penetrates through the sidcwalls 105 of the two tanks 102, 103, via an opposed pair of the through-holes 105a of the two tanks 102, 103. Specifically, one end 104a of the tube 104A is disposed within the inlet-side tank 102, and the other end 104a of the tube 104A is disposed within the outlet-side tank 103. In this state, the tube 104A is fixed to the two tanks 102, 103 in such a manner that a portion thereof inserted in the pair of through-holes 105a is fixed to the sidewalls 105 of the two tanks 102, 103 by fixing means such as brazing. In the same manner, the tube 104B is fixed to the two tanks 102, 103.
The target fluid is led into the inlet-side tank 102 through the non-depicted inlet port, and after being led from the inlet-side tank 102 to the outlet-side tank 103 via the tubes 104A, 104B, lead out of the outlet-side tank 103 through the non-depicted outlet port. The target fluid is cooled by heat exchange with outside air in the course of passing through the tubes 104A, 104B.
However, in the heat exchanger 101, the tube 104A nearest to the end walls 106 of the two tanks 102, 103 is likely to crack in the portion thereof fixed to the two tanks 102, 103, thereby leading to leakage of the target fluid from the cracked area. The reason is considered as follows.
In the inlet-side tank 102, the target fluid led through the non-depicted inlet port is moved in the longitudinal direction, and finally led into the tubes 104A, 104B. However, in the course of the above movement, when the target fluid reaches the end wall 106 and becomes unable to go straight ahead any more, it is turned toward the end 104a of the tube 104A nearest to the end wall 106, as indicated by the arrowed line Y3. Due to the above flow, the end 104a of the tube 104A is applied with a force from the target fluid and thereby inclined about a base of the end 104a serving as a supporting point, as indicated by the arrowed line Y4, and, accordingly, a crack is formed in the fixed portion (particularly, a part of the fixed portion on the side of the end wall 106).
On the other hand, the target fluid led into the outlet-side tank 103 via the tubes 104A, 104B is moved in a longitudinal direction of the outlet-side tank 103, and finally led to the non-depicted outlet port. However, in the course of the above movement, when the target fluid reaches the end wall 106 and becomes unable to go straight ahead any more, it is turned toward the end 104a of the tube 104A nearest to the end wall 106, as indicated by the arrowed line Y5. Due to the above flow, the end 104a of the tube 104A is applied with a force from the target fluid and thereby inclined about a base of the end 104a serving as a supporting point, as indicated by the arrowed line Y6, and, accordingly, a crack is formed in the fixed portion.
Another reason for the formation of a crack in the fixed portion is considered that the ends 104a of the tube 104A receive forces from the flows of the target fluid indicated by the arrowed lines Y3, Y5, and, due to these forces, a peripheral wall of the tube 104A is concavely deformed.